I don't think it's unreasonable to say that Boston, Cleveland, and OKC are in a class of their own. Houston may not be far behind and need more time.
Total wins for the top 10 teams in the league record wise against each other. BOS CLE OK got 40+ wins total. NY MEM DEN HOU got 35-37, rest got 32-35.
CLE OKC BOS NY MEM DEN HOU LAL IND MIL Record Games
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CLE 1-1 1-2 2-0 1-0 2-0 0-2 2-0 1-1 0-0 10-6 16
OKC 1-1 1-0 2-0 2-0 1-1 2-1 1-0 1-0 1-0 12-3 15
BOS 2-1 0-1 3-0 0-1 1-0 1-1 0-1 1-2 3-0 11-7 18NY 0-2 0-2 0-3 1-0 2-0 1-1 0-1 2-1 2-0 8-10 18
MEM 0-1 0-2 1-0 0-1 1-1 1-3 1-2 0-0 2-0 6-10 16
DEN 0-2 1-1 0-1 0-2 1-1 0-1 1-1 0-0 0-0 3-9 12
HOU 2-0 1-2 1-1 1-1 3-1 1-0 1-0 1-0 0-1 11-6 17
LAL 0-2 0-1 1-0 1-0 2-1 1-1 0-1 1-0 0-0 6-6 12
IND 1-1 0-1 2-1 1-2 1-1 0-0 0-1 0-1 0-2 5-8 13
MIL 0-2 0-1 0-3 0-2 0-2 0-0 1-0 0-0 2-0 3-10 13